Additive Force Device For Drug Delivery Pen For Intradermal Medication Injection

ABSTRACT

An additive force device ( 111 ) is connectible with a drug delivery device ( 100 ) to increase the amount of force exerted by a user on the dose setting knob ( 24 ) to facilitate injection. The additive force device ( 111 ) includes a first spring ( 121 ) and a loading barrel ( 135 ) connected to the first spring ( 121 ) for storing torque therein. A ratchet assembly ( 129 ) is connected to the loading barrel ( 135 ) and to the first spring ( 121 ). The ratchet assembly ( 129 ) has a first position in which torque is stored in the first spring ( 121 ) and a second position in which torque is released from the first spring ( 121 ). An inner barrel ( 133 ) is connected to the ratchet assembly and to the drug delivery device ( 100 ). The inner barrel ( 133 ) transmits the stored torque from the first spring ( 121 ) to the drug delivery device ( 100 ) to increase an injection force thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application Ser. No. 61/193,314, filed Nov. 17, 2008, theentire disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to a drug delivery pen for anintradermal medication injection. More particularly, the presentinvention generally relates to an additive force device for a drugdelivery pen that facilitates intradermal medication injection. Stillmore particularly, the present invention provides a drug delivery penhaving an additive force device that supplies additional injection forceto the pen knob of the drug delivery pen to facilitate an intradermal ofother high pressure injection of medication.

BACKGROUND OF THE INVENTION

Insulin and other injectable medications are commonly given with drugdelivery pens, whereby a disposable pen needle assembly is attached tofacilitate drug container access and allow fluid egress from thecontainer through the needle into the patient.

As technology and competition advance, driving the desire for shorter,thinner, less painful, and more efficacious injections, the design ofthe pen needle assembly and parts thereof becomes more and moreimportant. Designs need to proactively address ergonomically improvinginjection technique, injection depth control and accuracy, the abilityto be safely used and transported to disposal, and protection againstmisuse while maintaining the ability to be economically manufactured ona mass production scale.

The assembly and operation to a typical drug delivery pen, as shown inFIGS. 1 and 2, is described in U.S. Patent Application Publication No.2006/0229562, published on Oct. 12, 2006 and in U.S. Pat. No. 6,248,095,issued on Jun. 19, 2001, both of which are hereby incorporated byreference in their entirety.

Drug delivery pens, such as the exemplary drug delivery pen 100 shown inFIGS. 1 and 2, are designed for subcutaneous injections and typicallycomprise a dose knob/button 24, an outer sleeve 13, and a cap 21. Thedose knob/button 24 allows a user to set the dosage of medication to beinjected. The outer sleeve 13 is gripped by the user when injectingmedication. The cap 21 is used by the user to securely hold the drugdelivery pen 100 in a shirt pocket, purse or other suitable location andprovide cover/protection from accidental needle injury.

FIG. 2 is an exploded view of the drug delivery pen 100 of FIG. 1. Thedose knob/button 24 has a dual purpose and is used both to set thedosage of the medication to be injected and to inject the dosedmedicament via the leadscrew 7 and stopper 15 through the medicamentcartridge 12, which is attached to the drug delivery pen through a lowerhousing 17. In standard drug delivery pens, the dosing and deliverymechanisms are all found within the outer sleeve 13 and are notdescribed in greater detail here as they are understood by thoseknowledgeable of the prior art. The distal movement of the plunger orstopper 15 within the medicament cartridge 12 causes medication to beforced into the needle 11 of the hub 20. The medicament cartridge 12 issealed by septum 16, which is punctured by a septum penetrating needlecannula 18 located within the hub 20. The hub 20 is preferably screwedonto the lower housing 17, although other attachment means can be used,such as attaching to the cartridge. To protect a user, or anyone whohandles the pen injection device 100, an outer cover 69, which attachesto the hub 20, covers the hub. An inner shield 59 covers the patientneedle 11 within the outer cover 69. The inner shield 59 can be securedto the hub 20 to cover the patient needle by any suitable means, such asan interference fit or a snap fit. The outer cover 69 and the innershield 59 are removed prior to use. The cap 21 fits snugly against outersleeve 13 to allow a user to securely carry the drug delivery pen 100.

The medicament cartridge 12 is typically a glass tube sealed at one endwith the septum 16 and sealed at the other end with the stopper 15. Theseptum 16 is pierceable by a septum penetrating cannula 18 in the hub20, but does not move with respect to the medicament cartridge 12. Thestopper 15 is axially displaceable within the medicament cartridge 12while maintaining a fluid tight seal.

The backpressure in subcutaneous injections is not very large, while thebackpressure associated with intradermal injections may be many timesgreater than that of subcutaneous injections. For example, thebackpressure often exceeds 200 psi for an intradermal injection, whilethe backpressure for a subcutaneous injection is generally in the rangeof 30-50 psi. Thus, a need exists for a drug delivery pen that has ahigh mechanical gain to reduce thumb forces required to overcome theinitial high breakout force in the cartridge during an intradermalinjection.

Existing intradermal drug delivery devices require a large force toinject the medication because of back pressure created from theintradermal layer, thereby making the intradermal injection difficult.Therefore, a need exists for a drug delivery pen that has an additiveforce device to add to the user's input force of depressing theinjection button to allow an intradermal injection to be made with a lowuser force.

Accordingly, a need exists for a drug delivery pen that facilitatesintradermal medication injection.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, an additive forcedevice for drug delivery is provided that supplies additional forceduring an injection by adding force to the user's force, therebyfacilitating the intradermal medication injection.

The additive force device includes an energy storage device, such as atorsion spring or a compression spring, used with a drug delivery pen,or other similar device, to aid a user during an injection by supplyingadditional force to a plunger of the drug delivery pen. Preferably, theadditional force is supplied when a preset force is exceeded. Theadditive force device is loaded with a twist of a barrel, and then thedose is set on the drug delivery pen. The drug delivery pen is then usedin its normal manner. When the force exerted by the user rises above apredetermined value, for example, five pounds or any other suitableergonomic value, a mechanism releases the energy stored in the energystorage device to turn the pen's mechanism to effectively add force tothe force exerted by the user.

Objects, advantages, and salient features of the invention will becomeapparent from the following detailed description, which, taken inconjunction with the annexed drawings, discloses exemplary embodimentsof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above benefits and other advantages of the various embodiments ofthe present invention will be more apparent from the following detaileddescription of exemplary embodiments of the present invention and fromthe accompanying figures, in which:

FIG. 1 is a perspective view of an assembled drug delivery pen;

FIG. 2 is an exploded perspective view of the components of the drugdelivery pen of FIG. 1;

FIG. 3 is a perspective view in cross section of an additive forcedevice for a drug delivery pen for intradermal medication injection;

FIG. 4 is an exploded perspective view of the additive force device ofFIG. 3;

FIG. 5 is a front elevational view of the additive force device of FIG.3 prior to a dose being set;

FIG. 6 is a front elevational view in partial cross section of theadditive force device of FIG. 5;

FIG. 7 is a perspective view of the additive force device of FIG. 5;

FIG. 8 is a perspective view of the additive force device of FIG. 3after a dose has been set;

FIG. 9 is an exploded perspective view of the additive force device ofFIG. 3;

FIG. 10 is an illustration of the force input by a user and theresulting output force generated by a conventional drug delivery pen;

FIG. 11 is an illustration of the force input by a user and theresulting output force generated by a drug delivery pen to which anadditive force device according to an exemplary embodiment of thepresent invention has been connected;

FIG. 12 is a table of the user input force and the resulting outputforce generated by a conventional drug delivery pen;

FIG. 13 is a table of the user input force and the resulting outputforce generated by a drug delivery pen to which an additive force deviceaccording to an exemplary embodiment of the present invention has beenconnected;

FIGS. 14-16 are side and front elevational views and a perspective viewof a torsion spring;

FIGS. 17 and 18 are elevational views of a additive force device of FIG.3 connected to a drug delivery pen;

FIGS. 19 and 20 are exploded perspective views of the additive forcedevice and drug delivery pen of FIGS. 17 and 18;

FIGS. 21 and 22 are side elevational views of the additive force deviceconnected to a drug delivery pen of FIGS. 17 and 18;

FIG. 23 is a side elevational view in cross section of the additiveforce device and drug delivery pen of FIG. 22;

FIG. 24 is an enlarged elevational view in cross section of the additiveforce device of FIG. 23; and

FIG. 25 is an enlarged elevational view in cross section in which theadditive force device of FIG. 24 is rotated approximately 90 degrees.

Throughout the drawings, like reference numbers will be understood torefer to like parts, components and structures.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The following description and details of exemplary embodiments of thepresent invention are disclosed with reference to a typical drugdelivery pen 100, as shown in FIGS. 1 and 2. However, the additive forcedevice of the present invention may be used with any suitable drugdelivery pen. The pen may be provided with a subcutaneous patient needle11 as shown or with a shorter (approximately between 0.5-3 mm andpreferably approximately between 1.5-2 mm) intradermal patient needle.

In the exemplary embodiment of the present invention shown in FIGS.3-25, the additive force device 111 is connected to an existing drugdelivery pen 100 (FIGS. 1 and 2), as shown in FIGS. 17-25. An additiveforce device 111 is connectible with a drug delivery pen 100 to increasethe amount of force exerted by a user on the pen knob 24 to facilitateinjection. The additive force device 111 includes a first spring 121 anda loading barrel 135 connected to the first spring 121 for storingtorque therein. A ratchet assembly 129 is connected to the loadingbarrel 135 and to the first spring 121. The ratchet assembly has a firstposition in which torque is stored in the first spring 121 and a secondposition in which torque is released from the first spring 121. An innerbarrel 133 is connected to the ratchet assembly and to the drug deliverypen 100. The inner barrel 133 transmits the stored torque from the firstspring 121 to the drug delivery pen 100 to increase an injection forcethereof.

The additive force device 111 includes a button 161 connected to aloading barrel 135. A lower ratchet 151 is connected to the loadingbarrel 135. An upper ratchet 125 is connected to the lower ratchet 151.A first spring 121 is disposed between the loading barrel 135 and theupper ratchet 125. The upper ratchet 125 is connected to an inner barrel133. A second spring 127 is disposed between the inner barrel 133 andthe lower ratchet 151. An outer barrel 131 is connected to the innerbarrel 133 and to the knob 24 of the drug delivery pen 100. A fixingbarrel 145 is connected to the outer barrel 131 and to the drug deliverypen 100.

The button 161 has a substantially planar outer surface 163, as shown inFIG. 19. A protrusion 167 extends outwardly from an inner surface 165. Acircumferential rib 169 extends around the protrusion, as shown in FIG.20. The circumferential rib 169 facilitates securing the button 161 tothe lower ratchet 151.

The loading barrel 135 has an inner wall 181 and an outer wall 183. Agroove 184 extends axially along an inner surface of the inner wall 181and receives the rib 153 of the lower ratchet 151, thereby keying theloading barrel 135 to the lower ratchet 151. Preferably, a second grooveis disposed diametrically opposite the first groove 184 to receive thesecond rib of the lower ratchet 151.

The ratchet assembly 129 includes a lower ratchet 151 and an upperratchet 125. The lower ratchet 151 has a base 155 and a shaft 157extending outwardly therefrom. A rib 153 extends axially along an outersurface of the shaft 157. Preferably, a second rib is diametricallyopposed to the rib 153. A plurality of teeth 158 are disposed on anupper surface of the base 155.

The upper ratchet 125 has a base 191. A plurality of teeth 193 aredisposed on a lower surface of the base 191. The plurality of teeth 193of the upper ratchet 125 are adapted to engage the plurality of teeth158 of the lower ratchet 151. An arm 192 extends upwardly from the base191. Preferably, a second arm 192 is disposed diametrically opposite thefirst arm 192, as shown in FIG. 4. The arm 192 keys the upper ratchet125 to the inner barrel 133. A wall 194 extends upwardly from the base191 of the upper ratchet 125.

A first spring 121 is disposed between the upper ratchet 125 and theloading barrel 135. A first end 122 of the first spring 121 is securedto the wall 194 of the upper ratchet 125, as shown in FIG. 24. A secondend 124 of the first spring 121 is received by a surface 182 of theloading barrel 135. Preferably, the first spring 121 is a torsionspring, although any suitable spring may be used.

An inner barrel 133 preferably has a substantially cylindrical shape andhas an outer surface 144 and an inner surface 146, as shown in FIGS. 19and 20. Splines extend axially along a portion of the outer surface 146of the inner barrel 133. A base 147 is disposed within the inner barrel133, as shown in FIGS. 24 and 25. A plurality of notches 149 aredisposed on the inner surface 146 of the inner barrel and are adapted tokey the inner barrel to corresponding notches 25 (FIG. 1) of the penknob 24 of the drug delivery pen 100.

A second spring 127 is disposed between the lower ratchet 151 and theinner barrel 133, as shown in FIGS. 24 and 25. A first end 172 of thesecond spring 127 engages the lower ratchet 151. A second end 174 of thesecond spring 127 is received by the base 147 of the inner barrel 133.Preferably, the second spring 127 is a compression spring, although anysuitable spring may be used. The second spring 127 biases the lowerratchet 151 toward the upper ratchet 125 such that the teeth of thelower ratchet engage the teeth of the upper ratchet.

An outer barrel 131 has a preferably substantially cylindrical shape andhas an outer surface 136 and an inner surface 138, as shown in FIGS. 19and 20. Flexible buttons 123 are movably formed in the outer barrel 131.A rib 148 extends axially along an outer surface 136 of the outer barrel131. Preferably, a second rib is disposed diametrically opposite thefirst rib 148.

A fixing barrel 145 has a base 132, as shown in FIG. 20. A wall 134extends upwardly from the base 132. A groove 136 extends axially alongan inner surface of the wall 134. Preferably, a second groove isdisposed diametrically opposite the first groove 136. The groove 136receives the rib 148 of the outer barrel, thereby keying the outerbarrel to the fixing barrel 145. A pair of flexible legs 138 extendsdownwardly from the base and are adapted to secure the additive forcedevice 111 to the drug delivery pen. Preferably, a window 171 is formedbetween the flexible legs 138 such that a dose setting window 31 of thedrug delivery pen 100 is visible to a user after the additive forcedevice 111 is connected to the drug delivery pen 100, as shown in FIG.21.

Assembly and Operation

Energy is stored in an energy storage device, such as a torsion springor a compression spring. The inner barrel 133 is attached to the penknob 24 of the drug delivery pen 100 to transmit torque generated by theadditive force device 111 to the drug delivery pen 100. Preferably, theinner barrel 133 is rigidly keyed to the outer sleeve 13 of the drugdelivery pen 100. The outer sleeve 13 of the drug delivery pen 100 ispreventing from rotating while torquing the barrel 135 of the forceadditive device 111 and storing energy (torque) in the torsion spring121 by the engagement of the splines of the buttons 123 and the innerbarrel 133. The torsion spring energy is held by a one-way ratchetsystem that is held together by the second spring 127. The fixing barrel145 is attached to the outer sleeve 13 of the drug delivery pen 100 inany suitable manner, such as by a snap connect or friction fit. As shownin FIGS. 24 and 25, inwardly extending tabs 140 of the fixing barrel 145may secure the fixing barrel to the drug delivery pen 100 by a snapconnect.

Although not limited thereto, the following description refers to thefirst spring 121 being a 1.4 in-lbs torsion spring 121 as shown in FIGS.14-16. The first spring 121 may be loaded before or after connecting theadditive force device 111 to the drug delivery pen 100 by twisting theloading barrel 135 while pressing the cantilever buttons 123. As theuser grasps the loading barrel 135 and the buttons 123 are being flexedinwardly, the splines 142 of the outer barrel 131 engage thecorresponding splines 143 of the inner barrel 133 to prevent the innerbarrel 133 from rotating as the loading barrel 135 is rotated to loadthe torsion spring 121. The loading barrel 135 is keyed to the lowerratchet 151 by the groove 184 and rib 153. The compression spring 127applies a constant biasing force on the lower ratchet 151 to contact thelower ratchet 151 with the upper ratchet 125 such that the teeth of theupper and lower ratchets engage. The upper ratchet 125 is keyed to theinner barrel 133 by the arms 192 engaging openings 138 in the innerbarrel. By depressing the buttons 123, the splines of the outer barrel133 and the inner barrel 131 engage such that the inner barrel isprevented from rotating when the loading barrel 135 is rotated. Theplurality of teeth of the upper ratchet 125 slide over the plurality ofteeth of the lower ratchet 151, thereby creating an audible indicationthat the first spring is being energized.

After the additive force device 111 is connected to the drug deliverypen 100, the dose is set using the additive force device. The usergrasps and rotates the loading barrel 135 to set the desired dose. Thewindow 171 formed in the fixing barrel 145 allows the user to view thedose setting window 31 of the drug delivery pen. The fingers 123 are notflexed inwardly such that the pen knob 24 rotates with rotation of theloading barrel 135, thereby allowing the user to set the dose.

The loading barrel 135 is keyed to the lower ratchet 151 such that thelower ratchet rotates with the loading barrel. The plurality of teeth158 of the lower ratchet 151 engage the plurality of teeth 193 of theupper ratchet 125 because the second spring 127 biases the lower ratchetagainst the upper ratchet. The upper ratchet 125 is keyed to the innerbarrel 133 by the arms 192 engaging the inner barrel, as shown in FIG.25. The inner barrel 133 is keyed to the pen knob 24 such that rotationof the loading barrel 135 results in rotation of the pen knob 24.Accordingly, the rotation of the pen knob 24 moves the pen knob awayfrom the outer sleeve 13 of the drug delivery pen 100 as with normaloperation of the drug delivery pen.

Outward movement of the pen knob 24 causes the pen knob to push the base147 of the inner barrel 133 toward the button 161. The outer barrel 131is keyed to the fixing barrel 145 by the rib 148 and groove 136, suchthat the outer barrel 131 moves axially relative to the fixing barrel145. Accordingly, when the pen knob 24 moves outwardly, the resultingmovement of the inner barrel 133 moves the outer barrel 131 along theaxial groove 136 of the fixing barrel 145. The inner barrel 133 alsopushes the second spring 127, which pushed the lower ratchet 151 andupper ratchet 125 as well as the loading barrel 135 outwardly. Aninjection may now be made with the drug delivery pen 100.

To make an injection, the user pushes the button 161 of the additiveforce device 111 toward the drug delivery pen 100. The inner surface 165of the button 161 contacts the loading barrel 135 such that the loadingbarrel moves with the button 161. Inward movement of the loading barrel135 pushes the lower ratchet 151, which is keyed to the loading barrel,inwardly. The lower ratchet 151 and the upper ratchet 125 remain engagedsuch that rotation of the upper ratchet 125 is prevented and the energystored in the first spring 121 is not released. The lower ratchet 151pushes the compression spring 127, which in turn pushes on the base 147of the inner barrel 133. Inward movement of the inner barrel 133 resultsin inward movement of the pen knob 24, which is keyed to the innerbarrel 133, thereby administering medicament in accordance with normaloperation of the drug delivery pen 100.

When the force required to administer the medicament is greater than apredetermined preload, five pounds for example, the second spring 127compresses such that the lower ratchet 151 is disengaged from the upperratchet 125. When the plurality of teeth 158 of the lower ratchet 151disengage from the plurality of teeth 193 of the upper ratchet 125, theupper ratchet 125 is free to rotate. The energy stored in the firstspring 121 is released and causes the upper ratchet 125 to rotate. Therotation of the upper ratchet 125 causes rotation of the inner barrel133, which is keyed to the upper ratchet 125. The rotation of the innerbarrel 133 rotates the pen knob 24 because the pen knob 24 is keyed tothe inner barrel. Accordingly, the torque stored in the first spring 121is transmitted to the pen knob 24, thereby adding to the user inputforce. The medicament is administered with the drug delivery pen inaccordance with normal operation thereof.

The second end 124 of the first spring 121 is connected to the loadingbarrel 135. The inward movement of the loading barrel 135 (resultingfrom the button 161 being pushed inwardly) causes the splines 137 of theloading barrel 135 to engage the splines 141 of the outer barrel 131.The splines 137 of the loading barrel 135 and the splines 141 of theouter barrel 131 are initially spaced apart by the second spring 127.The splines 137 of the loading barrel 135 and the splines 141 of theouter barrel 131 engage when a user feels a high injection force. Theouter barrel 131 is keyed to the fixing barrel 145, which is in turnkeyed to the drug delivery pen 100. Accordingly, the loading barrel 135is prevented from rotating such that the torque is delivered to theupper ratchet 125.

The torsion supplied is translated to a linear force by the drugdelivery pen's own mechanism and assists the user by supplying forceover and above the user's finger applied force, thereby allowing theuser to accomplish a more difficult intradermal medication injection.

The force additive device 111 according to exemplary embodiments of thepresent invention adds force to aid the user during injection preferablywhen the user experiences a high injection force. When the user does notexperience a high force, the force additive device 111 is not activatedand remains cocked until additional force is required. Some users maynot require the additional force, but the force additive device 111remains cocked should a high injection force be experienced. No actionis necessary when the force additive device 111 remains cocked.

The force additive device 111 applies force to aid the user at themoment when the user experiences the high injection force and not beforesuch time. Thus, the stored energy of the first spring 121 is appliedwhen it is needed most and preferably only at such time. Thisconfiguration optimally utilizes the torque stored in the first spring121 by applying the maximum amount of the stored energy to the highestpressure peak recorded on an intradermal pressure graph.

A color indicator window may be added to visually alert the user whenthe device is cocked. For example, the color green may be used toindicate that the force additive device is cocked and the color red toindicate that the force additive device needs to be cocked.

As shown in FIGS. 12 and 13, input forces and respective output forcesare shown for a drug delivery pen with (FIG. 13) and without (FIG. 12)the force additive device. For example, a drug delivery pen without theforce additive device outputs 7.14 pounds for a four pound input, asshown in FIG. 12. An output of approximately twenty pounds is requiredto overcome the intradermal back pressure. Adding a 1.4 in lb torque tothe pen barrel using the torsion spring of FIGS. 14-16 adds output forceto the drug delivery pen. As shown in FIG. 13, a 27.14 lb force isoutput when four pounds is input to a drug delivery pen 100 includingthe force additive device 111 such that the user input force ofapproximately 4 lb is sufficient to overcome intradermal back pressure.The results of FIGS. 12 and 13 are diagrammatically illustrated in FIGS.10 and 11, respectively.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the scope of the present invention. Thedescription of exemplary embodiments of the present invention isintended to be illustrative, and not to limit the scope of the presentinvention. Various modifications, alternatives and variations will beapparent to those of ordinary skill in the art, and are intended to fallwithin the scope of the invention as defined in the appended claims andtheir equivalents.

1. An additive force device for use with a drug delivery device,comprising: a first spring; a loading barrel connected to said firstspring for storing torque therein; a ratchet assembly connected to saidloading barrel and to said first spring, said ratchet assembly having afirst position in which torque is stored in said first spring and asecond position in which torque is released from said first spring; andan inner barrel connected to said ratchet assembly and to the drugdelivery pen, said inner barrel transmitting the stored torque from saidfirst spring to the drug delivery device to increase an injection forcethereof.
 2. The additive force device for use with a drug deliverydevice of claim 1, wherein said ratchet assembly includes a lowerratchet and an upper ratchet, each of said lower and upper ratchetshaving a plurality of teeth for engagement therebetween.
 3. The additiveforce device for use with a drug delivery device of claim 2, whereinsaid lower ratchet is connected to said loading barrel.
 4. The additiveforce device for use with a drug delivery device of claim 3, whereinsaid upper ratchet is connected to said first spring.
 5. The additiveforce device for use with a drug delivery device of claim 4, wherein asecond spring is disposed between said inner barrel and said lowerratchet to bias said lower ratchet against said upper ratchet.
 6. Theadditive force device for use with a drug delivery device of claim 5,wherein said lower and upper ratchets are engaged when said ratchetassembly is in said first position, and said lower and upper ratchetsare spaced apart when said ratchet assembly is in said second position.7. The additive force device for use with a drug delivery device ofclaim 6, wherein said inner barrel is disposed in an outer barrel, saidouter barrel having a flexible button for engaging said inner barrelwhen torque is being supplied to said first spring to substantiallyprevent movement of said inner barrel and said lower ratchet.
 8. Theadditive force device for use with a drug delivery device of claim 1,wherein said first spring is a torsion spring.
 9. The additive forcedevice for use with a drug delivery device of claim 1, wherein saidsecond spring is a compression spring.
 10. The additive force device foruse with a drug delivery device of claim 9, wherein said second springhas a preload of approximately five pounds.
 11. The additive forcedevice for use with a drug delivery device of claim 7, wherein a fixingbarrel is connected to said outer barrel and to said drug deliverydevice, said outer barrel being axially movable within said fixingbarrel.
 12. The additive force device for use with a drug deliverydevice of claim 11, wherein said loading barrel being engaged with saidouter barrel when said ratchet assembly is in said second position tosubstantially prevent movement of said loading barrel.
 13. A medicamentdelivery device, comprising: a drug delivery pen having a dose settingknob at an end thereof; and an additive force device connected to saiddose setting knob end of said drug delivery pen, said additive forcedevice including a first spring; a loading barrel connected to saidfirst spring for storing torque therein; a lower ratchet connected tosaid loading barrel; an upper ratchet connected to said lower ratchetand to said first spring; an inner barrel connected to said upperratchet and to the drug delivery pen, wherein torque is stored in saidfirst spring, when said upper and lower ratchets are engaged torque isprevented from being released from said first spring, and when saidupper and lower ratchets are separated said inner barrel transmits thestored torque from said first spring to the drug delivery pen toincrease an injection force thereof.
 14. The medicament delivery deviceof claim 13, wherein said first spring is a torsion spring.
 15. Themedicament delivery device of claim 13, wherein a second spring isdisposed between said inner barrel and said lower ratchet to bias saidlower ratchet against said upper ratchet.
 16. The medicament deliverydevice of claim 13, wherein said inner barrel is disposed in an outerbarrel, said outer barrel having a flexible button for engaging saidinner barrel when torque is being supplied to said first spring tosubstantially prevent movement of said inner barrel and said lowerratchet.
 17. A method of amplifying an injection force of a drugdelivery device, comprising the steps of: storing energy in an additiveforce device; connecting the additive force device to the drug deliverydevice; setting a dose of medicament to be administered; and releasingthe stored energy of the additive force device to amplify the injectionforce of the drug delivery device.
 18. The method of amplifying aninjection force of a drug delivery device of claim 17, wherein theenergy is stored in the additive force device before the additive forcedevice is connected to the drug delivery device.
 19. The method ofamplifying an injection force of a drug delivery device of claim 17,wherein the additive force device is connected to the drug deliverydevice before the dose is set.
 20. The method of amplifying an injectionforce of a drug delivery device of claim 17, wherein the dose is setwith the additive force device.